In a hydraulic brake booster pressurized fluid from an inlet port is communicated to an accumulator. The pressurized fluid is also communicated upon operator actuation of a spool valve to a pressure chamber wherein the pressurized fluid urges a piston to move within the hydraulic brake booster housing to effect a brake application.
When the actuation of the spool valve fails to communicate pressurized fluid to the pressure chamber, further brake pedal application by a motor vehicle operator urges a lever into engagement with a check valve to open communication between the accumulator and pressure chamber. Consequently, pressurized fluid is communicated to the pressure chamber to effect a brake application.
In order to charge the accumulator and to communicate the accumulator with the pressure chamber, the hydraulic brake booster housing includes a bore extending from the inlet port to the pressure chamber and intersecting the accumulator. Within this bore are disposed a charging valve and a check valve. The charging valve of the prior art communicates pressurized fluid from the inlet port to the accumulator when the force of the pressure at the inlet port is greater than the force of the pressure within the accumulator plus the resilient force of a spring urging the charging valve to a closed position. The check valve of the prior art normally closes communication between the accumulator and the pressure chamber as a result of the force of the pressure within the accumulator and the resilient force of the spring urging the check valve to a closed position.